1. Field of the Invention
This invention relates to a novel adhesion structure using an adhesive composed of a thermosetting resin composition and a method of producing the same. More particularly, it relates to adhesion structures having improved strength, heat resistance and waterproofness or an electrical conductivity, or carbonaceous or graphitic adhesion structures.
2. Related Art Statement
As an adhesive made from a thermosetting resin, there have hitherto been known, for example, unsaturated polyester adhesives, phenolic resin adhesives, epoxy resin adhesives, polyisocyanate adhesives, bismaleimide adhesives, thermosetting polyamide adhesives and so on.
As a technique for chemically bonding the adhesive to an adherend, Japanese Patent Application Publication Nos. 36-17081 and 37-2970 disclose that chromium aminoacetate and silane a coupling agent are an effective surface treating agent for an adherend such as glass.
Furthermore, when using an epoxy resin as an adhesive, the adhesive strength is dependent upon the amount of hydroxyl groups existent on the surface of the adherend or in the epoxy resin and hydrogen bonds between the hydroxyl groups existent on the adherend and the epoxy resin contributes substantially to the adhesive force, as disclosed in K. Kanamaru, Adhesion and Adhesives, Dai Nippon Tosho Printing Co., Ltd., 1978, page 128.
In this article (page 133), it is also disclosed that when using a polyisocyanate as an adhesive, hydrogen atoms existent in the surface of wood, hydroxyl groups existent in the surface of synthetic fibers, amino group existent in the surface of leather or the like are strongly bonded to the adhesive through urethane or urea bonds.
A heat-resistant adhesive made from an imide modified epoxy resin is disclosed in Japanese Patent laid open patent application Nos. 59-166,531 and 60-32821. While, a heat-resistant adhesive made from a bismaleimide is disclosed in Japanese laid open patent application No. 57-2328.
If it is intended to produce an adhesion structure having electrical conductivity by using an adhesive made from a conventionally known thermosetting resin, since the adhesive itself has no electrical conductivity, it is required to incorporate a conductive filler into the adhesive.
As a carbonaceous or graphitic adhesive, there are known some commercially available ones, but their details are not presently available.
Such adhesives are considered to be roughly classified as follows:
(1) a mixture of carbon or graphite or its precursor as an aggregate and a B-stage resin of a thermosetting resin such as phenolic resin, epoxy resin, furan resin or the like; and
(2) a mixture of the same mixture as described in the above item (1) and a petroleum or coal tar pitch.
Among them, V58a (trade name, made by Sigri Elk. GmbH) is commercially available as the mixture (1), while New Coat GC (trade name, made by Dylon Industry Inc.) is commercially available as the mixture (2). Further, a tar-containing adhesive for refractory brick is disclosed in Japanese laid open patent application No. 54-114,543.
Among the aforementioned adhesives each made from the thermosetting resin, the unsaturated polyester adhesive, phenolic resin adhesive, epoxy resin adhesive, polyisocyanate adhesive, thermosetting polyamide adhesive and so on have drawbacks in that the heat deformation temperature is low at the hardening state and the storage stability is poor. Further, the thermosetting polyamide adhesive is expensive. In the technique of introducing the chemical bonding as disclosed in Japanese Patent Application Publication Nos. 36-17081 and 37-2927, the adherend is limited to the glass composition and the adhesive component is limited to the epoxy resin, so that there is still a problem with the heat resistance.
When the epoxy resin is used as an adhesive component, the adhesion is dominantly contributed by hydrogen bonding between hydroxyl groups, so that the bonding force is weak as compared with the chemically covalent bond and the strength is poor.
The use of polyisocyanate has drawbacks as it is poisonous, inconvenient to handle and very sensitive to humidity during storage.
When bismaleimide is used as an adhesive component, the heat resistance is excellent, but the adhesive strength is weak as compared with that of the epoxy resin adhesive. As the heat resistance, the blistering time in a solder bath at 300.degree. C. under normal pressures was within a range of 70-80 minutes.
In the carbonaceous or graphitic adhesives (1), the carbonization yield in the hardened resin is low and the carbonization shrinkage of the adhesive relative to the adherend is very large. Further, if the aggregate is not added to the adhesive, the adhesive strength after carbonization is remarkably low. Moreover, the thickness of the adhesive is dependent upon the grain size of the aggregate, so that a high dimensional accuracy is not obtained. Since the thermal expansion coefficient of the adhesive layer after carbonization or graphitization is unadjustable, the resulting adhesion structure is weak to thermal shock.
In the carbonaceous or graphitic adhesives (2), the carbonization yield of the thermosetting resin is low, which is intended to be solved by adding tar or pitch having a high carbonization yield. Since the pitch naturally has a thermoplasticity, however, the amount of pitch added is restricted to a certain level. If the amount of the pitch is too large, the adhesive layer is foamed or softened at the carbonization step, and the adhesive strength is low. Furthermore, the thermal expansion coefficient of the adhesive layer after carbonization or graphitization can not be controlled, so that the thermal shock resistance of the adhesive joint is considerably low.
In the adhesives (1) and (2), the bonding between the adherend and the adhesive is dependent upon the physical adhesion (i.e. anchor effect), but does not positively introduce the chemical bonding, so that it can not be said that the properties such as thermal shock resistance, dimensional stability, strength, modulus of elasticity, toughness and so on are sufficiently obtained in the resulting adhesion structure.